When buying AR-coated solar glass, transmittance is usually one of the first numbers checked.
A sample comes in, the optical result meets the requirement, and the product is approved.
But solar glass does not stay in that condition forever.
After the module is installed, the glass will be exposed to dust, rain, sunlight and temperature changes. In some locations it will also be cleaned regularly, sometimes with brushes or other mechanical equipment.
So there is another number worth asking about.
How much of the original optical performance is still there after use?
New glass and used glass are not the same situation
A new AR-coated glass sample is easy to test.
The surface is clean and the coating has not been through repeated cleaning or outdoor exposure.
The initial transmittance gives us a useful starting point, but it is only a starting point.
For example, two AR-coated glasses may have very similar transmittance when they are new. After repeated abrasion or cleaning, their results may no longer be so close.
That difference is what durability testing is trying to find.
Cleaning is one of the things worth paying attention to
Solar modules in dusty areas may need frequent cleaning.
And cleaning is not always gentle.
Water and a soft cleaning method create one type of contact. A rotating brush working against a dusty surface creates another.
If sand or hard particles are present, the cleaning process can put additional mechanical stress on the surface.
This is why a supplier saying that an AR coating is "scratch resistant" is not really enough information.
A buyer should know how that conclusion was reached.
How many cycles?
What type of brush?
Wet or dry?
Was an abrasive material used?
What happened to the transmittance afterward?
Those details make the test result much more useful.
The project location changes the question
A solar project in a desert environment doesn't face exactly the same conditions as one near the coast.
Dust and sand may be the bigger concern in one location.
Salt, humidity or frequent condensation may be more relevant somewhere else.
Agricultural projects can have different surface contamination again.
There is no single laboratory test that can reproduce every outdoor condition.
For this reason, durability data is more useful when it is connected to the actual project.
If the customer expects frequent mechanical cleaning, the abrasion performance deserves more attention.
If the project is in a high-soiling area, the cleaning method should be considered together with the coating.
A coating can change without looking badly damaged
This is another point that is easy to miss.
After testing or cleaning, a coating may show visible scratches, colour differences or local changes.
But visual inspection does not tell the whole story.
A surface can look acceptable while the measured optical result has changed.
The opposite can happen as well. A small visible mark may have very little influence on the overall optical performance.
So when durability is being evaluated, photographs are useful, but they should be supported by actual optical measurements.
Transmittance before testing.
Transmittance after testing.
And, where required, reflectance or other agreed optical parameters.
That comparison gives a much clearer picture.
Laboratory performance is not the same as production consistency
There is one more thing buyers should separate.
A durability test normally uses selected specimens.
A production order may contain thousands of pieces.
The question then becomes whether the manufacturer can keep the coating condition stable from one production batch to another.
Glass surface preparation, coating application, curing and production conditions can all influence the finished coating.
A good laboratory result is valuable.
But repeatable production is what matters when the same product is ordered again and again.
What should buyers look at?
For AR-coated solar glass, I would pay attention to these points:
Initial transmittance and reflectance
How the optical values were measured
Coating condition before and after testing
Cleaning or abrasion conditions
Number of test cycles
Optical performance after exposure
Coating uniformity
Batch-to-batch consistency
IEC 62805-2 provides measurement methods for transmittance and reflectance of photovoltaic glass, including AR-coated glass. For procurement, keeping the measurement conditions comparable is important when evaluating changes between samples or production batches.
At MIGO GLASS, we see AR-coated solar glass as more than a product with a high initial transmittance number.
The first test tells you how the glass performs when it is new.
Durability testing gives some idea of what happens after stress.
Production consistency tells you whether the same performance can be supplied repeatedly.
For a PV project expected to operate for many years, all three are worth looking at.
A high initial transmittance is a good starting point. Retained optical performance is what makes the specification more meaningful over the long term.
